Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...293..240b&link_type=abstract
Astronomy and Astrophysics 293, 240-251 (1995)
Astronomy and Astrophysics
Astrophysics
16
Sun: Infrared, Sun: Chromosphere, Sun: Faculae, Plages, Sun: Magnetic Fields, Sun: Photosphere
Scientific paper
The MgI 12.32μm line is a prime diagnostic for studying upper photospheric magnetic fields on the Sun. We study for the first time its behavior using flux-tube models with magnetic field strengths and filling factors characteristic of solar plage in order to establish the line's capabilities for measuring plage magnetic fields. We show that this line is only moderately sensitive to the range of temperatures expected for solar plages, including the chromospheric temperature rise. This low sensitivity considerably enhances this line as a magnetic field diagnostic for the upper photosphere of plages. We find that besides being highly sensitive to the field strength in flux tubes, the shape and Zeeman splitting of this line are almost equally sensitive to the magnetic filling factor at the flux-tube base. This combined sensitivity leads to the large range of profile shapes observed in plages. Not only can the 12μm emission lines be used to determine the sub-spatial-resolution distribution of flux-tube field strengths, but also the sub-spatial-resolution distribution of filling factors (i.e. they can provide an estimate of the "clumpiness" of the flux-tube distribution on a small scale). We also provide evidence that simple two-component modeling of magnetic flux tubes, without taking into account the height-dependence of the flux-tube size, may lead to erroneous conclusions in the case of the MgI 12μm lines, and that at least 1.5-D computations are required to adequately model these lines in magnetic flux tubes. Computations also show that standard flux-tube models simultaneously reproduce the observed splitting of the g=3 FeI lines at 1.5648μm (formed in the low photosphere) and at 525.02nm (middle photosphere), as well as of the 12.32μm emission line (upper photosphere). Our computations thus support the currently standard view that solar plages are composed of flux tubes with kGauss fields in the lower and mid photosphere, and that the thin-tube approximation is an adequate representation of the magnetic stratification in these flux tubes.
Bruls H. M. J. J.
Solanki Sami K.
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